1. Field of the Invention
The present invention relates to tilt sensor or tiltmeter.
2. Description of Related Art
A tilt sensor or tiltmeter measures how far the meter or sensing device has tilted by the position of, for example, a bubble in a fluid against a curved upper surface. Unlike a simple carpenter""s level, a more sophisticated tiltmeter measures tilt by comparing the impedance of the fluid (which is very sensitive to the position of the bubble) between a centrally located excitation electrode on the bottom of the sensor and two output electrodes on opposite sides of the top of the sensor.
In some applications, it is important to detect how far from vertical (or horizontal) the object of measure (e.g., an apparatus to which the tiltmeter is attached) has leaned. In this case, the sensor must be precisely aligned with the appropriate axis of an apparatus, and the apparatus must, in turn, be precisely aligned in a vertical (or horizontal) direction. In other situations, as in the present invention, it is not necessary for the tiltmeter to measure the absolute angle made between the apparatus and the vertical (or horizontal). In these situations, the tiltmeter need only measure changes in the angle, having a certain minimum angular change. For example, it is important to know how far earth formations may have slipped and how much the earth may have tilted.
In the oil industry, oil is often produced from subterranean reservoirs via wells wherein water is pumped to create fractures that allow the oil to flow into the well from greater distances from the wellbore. Tiltmeters are utilized to determine the location and size of these fractures. An array of tiltmeters near the surface can determine the azimuth and dip angle of the fracture. A vertical array of tiltmeters placed in a near-by oil well can determine the height of the fracture. Knowledge of the height of the fracture during fracture formation allows a producer to suspend the pumping operation if the fracture grows out of the oil bearing rock. Such knowledge is especially important if the layer above the oil bearing layer is an aquifer.
Present tools for a vertical array can only self-level themselves if installed in a well that is within less than about (plus or minus) 7 degrees from vertical and/or require extended periods of time for one to adjust to such tilts. Many wells presently have deviations of much greater than 7 degrees and a need exists to measure such tilting action in an accurate and expedient manner.
Briefly, the invention is related to a tilt sensor device having at least a pair of tilt sensors wherein each sensor of the pair is orthogonally disposed to the other. The device has means for rotating each sensor of each pair about the longitudinal axis of the other sensor such that each sensor of the device can be leveled relative to horizontal, and that both leveling and collection of tilt output signals from such a device can be achieved in an expedient manner.
The device is useful as a two-longitudinal axis tiltmeter that can be lowered into well boreholes to monitor hydraulic fractures, especially during production of subsurface materials from a subterranean reservoir. Advantages of the present tilt sensor device include uses at essentially all angles of inclination from the horizontal (or from vertical) and (provided there is an inclination to a wellbore) the device can always be aligned along the axis of inclination of a wellbore. In the latter use, a separate mechanism for determining the orientation of the tool is not necessary, although a well can be xe2x80x9cloggedxe2x80x9d to determine the inclination at each depth, as well as other parameters.